Flaticon is the largest icon database in the world. With Flaticon for Gsuit (GSlides) you will have all the power of Flaticon in your Google Slides. You can search and add icons directly from Flaticon to your slides. No more "copy-paste" icons from the website to your slides. 

Open the add on, Add-on > Flaticon for Gsuit (GSlides) > Start

Search for Icons, and add Icons to your slides by clicking on them.